7.1 – STATIC CHARGE

OVERVIEW

Ancient Greece: when certain objects were rubbed (ex. amber) with wool or fur, they would attract lint and dust

“STATIC”: stationary or not moving

Static Charge (or static electricity): electric charges that can be collected and held in 1 place

EARLY THEORIES OF ELECTRICITY

Hypothesized that there were 2 “electricities” Rubbing materials like amber produces oneRubbing materials like glass produces the

other

Benjamin Franklin: hypothesized only 1 kind of “electrical fluid”

Performed experiments that caused a build-up of this electrical fluid Called the build-up of fluid “positive” or “+”Called the shortage of electrical fluid “negative”

or “-”

Scientists still uses plus and minus to refer to electrical charge,

but the meaning is

NOT the same as

Franklin’s

PARTICLES!

Modern theories about electricity are based on.....

REVIEW All matter is made up of tiny particles

called...ATOMS Nucleus: the centre of the atom

Contains protons and neutrons Neutrons: no charge Protons: positive charge Electrons: negative charge

If the # of protons and electrons is equal, the atom is uncharged or neutral!

In a solid material...

+ nucleus vibrates but remains in the centre of the atom

- electrons move around the energy shells outside the nucleus

Result: ALL solid materials are charged by the transfer of electrons!

IONS Ion: a charged atom Electron(s) removed...

Because a negative charge is removed the atom has more positive than negative charges

More protons than electrons = + overall charge

Electron(s) added...Because a negative charge is added the

atom has more negative than positive charges

More electrons than protons = - overall charge

SUMMARY

The movement, or transfer, of electrons from 1 atom to another changes the atom’s charge

When an atom loses electrons, it becomes positive

When an atom gains electrons, it becomes negative

FRICTION and ELELCTRON TRANSFER

Friction: occurs when 2 objects rub against each other Results in 1 object losing electrons and 1

object gaining electrons

See Figure 7.3 in Textbook!

INSULATORS and CONDUCTORS

Think about this!

When you rub one end of a neutral plastic rob with a paper towel, the end you rub would become charged. The other end would remain neutral!

The electrons you

added to the neutral

plastic by friction will

stay in one place

Insulators: materials that do not allow charges to move easily Electrons removed from one location on an

insulator are NOT replaced by electrons from another location

EX.: glass, plastics, ceramics and dry wood

Conductors: materials that allow electrons to travel freely Electrons from a charged items will spread

evenly throughout a conductorEX.: Metals (copper and aluminum)

Metals are good conductors because their atoms possess at least one easily transferable electron

Only insulators can retain a static chargeStatic electricity is charge that is held very

nearly fixed in one place Conductors allow charge to flow

MEASURING CHARGE

Neutral objects:

# of electrons = # of protonsSmallest negative charge it can possess is -1

(gain 1 electron)Smallest positive charge it can possess is +1

(lose 1 electron)

Coulomb (C): unit of electrical charge 1 C of charge equals the addition or

removal of Lightning Bolt = 5C to 25CPenny = 1 million coulombs of negative

charge ○ Doesn’t give you a massive static shock

because it also has about 1 million C of positive energy NEUTRAL

GENERATING STATIC CHARGE

Charging an object by friction happens in everyday lifeStatic electricity in the clouds produces

lightning (friction between hot air rising rapidly through cloud banks)

Scientists studying static charges need a special device that can produce large amounts of static charge in a laboratory

VAN de GRAAFF GENERATOR

Uses friction to produce a large static charge on a metal dome

Mechanics: A moving belt produces a static charge

at the base of the generator The belt carries the charge to the top

where it collects on the dome

Applications of Static Electricity

Many valuable uses in technologyPlastic sandwich wrap clings because of static

electricityUsed to decrease air pollution

○ Devices in chimneys use static charge to remove small particles of smoke/dust from the air

Air ionizers○ Remove electron particles from the air

Painting cars ○ Paint is given an electrical charge then sprayed

on the car’s body (charged particles will stick to the metal)

Dangers of Static Electricity

Fuel trucks must get rid of all static charge before they start pumping fuelAttach a cable (conductor) to the truck that will

transfer excess charge to the ground GROUNDING: allowing charge to flow into the Earth’s

surface (the Earth is large enough to accept charge without becoming charged)

Lightning strikes ○ Lightning rods are placed on top of buildings ○ The charge will pass through the rod to the ground

instead of through the building